1. Field of the Invention
This invention relates to a drum type washing machine provided with a turbidity sensor detecting a turbidity of wash liquid in an outer or water tub for determination of a soil degree of laundry or for other purposes.
2. Description of the Prior Art
Conventional automatic washing machines of the top loading type have been provided with a turbidity sensor detecting turbidity of wash liquid. For instance, U.S. Pat. No. 5,373,714 to Masatsugu Wada discloses a control device for an automatic washing machine of the top loading type provided with a turbidity sensor comprising a light emitting element and a light detecting element. The turbidity sensor is disposed in a drain hole through which wash liquid is discharged out of a water-receiving tub. The turbidity sensor detects a turbidity of the wash liquid flowing between a light emitting face and a light detecting face. The washing operation is controlled on the basis of the results of detection by the turbidity sensor. For example, the results of detection by the turbidity sensor are used to determine a degree of soil of laundry. A time period of the wash step is controlled on the basis of the determined soil degree.
Provision of the turbidity sensor has recently been proposed for drum type washing machines. The drum type washing machines comprise a water tub having a front opening and a drum-like rotating tub rotatably mounted in the water tub and having a front wall with an opening and a circumferential wall with a multitude of through holes. The drum type washing machine is usually controlled so as to carry out an automatic washing course in which wash, intermediate dehydration, rinse and final dehydration steps are automatically executed sequentially.
In the automatic washing machines of the top loading type, the wash liquid in the drain hole is substantially clear except in a draining operation. However, water scale, detergent component, etc. tend to easily adhere to the light emitting and detecting faces of the turbidity sensor during the drainage, whereupon the detection accuracy is reduced. Accordingly, it is difficult to employ the disposition of the turbidity sensor in the washing machine of the top loading type also in the drum type washing machine.
Therefore, an object of the present invention is to provide a drum type washing machine in which the turbidity of the wash liquid is detected by the turbidity sensor comprising the light emitting and detecting elements, the washing operation is controlled on the basis of the result of detection by the turbidity sensor, and a reduction in the detection accuracy of the turbidity sensor can be prevented.
The present invention provides a drum type washing machine comprising an outer cabinet, a water tub provided in the outer cabinet so as to be inclined downwardly rearward and having a rear wall, a generally drum-like rotating tub rotatably mounted in the water tub and having a rear wall, and a turbidity sensor detecting a turbidity of wash liquid in the water tub and disposed on a lower inside face of the rear wall of the water tub, the turbidity sensor including a light emitting element and a light detecting element.
According to the above-described construction, the turbidity sensor comprises the light emitting element and the light detecting element. Consequently, a cost reduction and simplification of the construction can be achieved. Further, the turbidity sensor is disposed on the lower inside face of the rear wall of the water tub such that the light emitting face and the light detecting face are located in the wash liquid in the water tub. That is, since the turbidity sensor directly detects the turbidity of the wash liquid in the water tub, the turbidity can be detected reliably and accurately. Additionally, since the wash liquid flows between the light emitting element and the light detecting element with rotation of the rotating tub, an amount of water scale, detergent component, etc. adherent to the light emitting and detecting faces is reduced and accordingly, a reduction in the detection accuracy can be prevented.
In a first preferred form, the turbidity sensor is disposed so as to be opposed to the rear wall of the rotating tub. Upon rotation of the rotating tub, a water flow is produced in a space between the rear walls of the water tub and the rotating tub. Particularly, a water flow is produced in the space where the rear walls of the water tub and the rotating tub are opposed to each other. This water flow has a higher flow speed than a water flow produced in a space defined between the inner face of the rear wall of the water tub and the circumference of the rear wall of the rotating tub. Consequently, since water scale and detergent component adherent to the light emitting and detecting faces are washed away by the water flow and accordingly, the detection accuracy of the turbidity sensor can further be prevented from being reduced.
Additionally, the water tub and the rotating tub are disposed to be inclined rearwardly downward. In this construction, the turbidity sensor is disposed in a dead space between a lower portion of the rear wall of the water tub and the outer cabinet. Consequently, the dead space can effectively be used.
In a first preferred form, the lower inside face of the rear will of the water tub is formed with a hollow outward protrusion in which the turbidity sensor is disposed. Consequently, a distance between the rear walls of the water tub and the rotating tub can be prevented from being increased.
In a second preferred form, the outer cabinet has a rear wall with an inspection hole formed therethrough so as to correspond to the turbidity sensor and with a lid mounted thereon so as to close and open the inspection hole, and the turbidity sensor is detachably attached through the inspection hole to the rear wall of the water tub. Consequently, the turbidity sensor can easily be inspected and repaired.
In a third preferred form, the turbidity sensor is located on the rear wall of the water tub so as to be circumferentially displaced from a lowest portion of the rear wall of the water tub, and wherein the turbidity sensor carries out a detecting operation when the rotating tub is rotated in the direction of displacement of the turbidity sensor. Upon rotation of the rotating tub, the wash liquid in the wash tub is centrifugally caused to rise in the rotational direction of the rotating tub such that the water level at the side in the water tub opposite to the direction of rotation of the rotating tub is decreased, and an amount of bubble is increased. Consequently, the turbidity of the wash liquid can be detected accurately and reliably.
In a fifth preferred form, the water tub and the rotating tub are disposed to be inclined rearwardly downward. In this construction, the turbidity sensor is disposed in a dead space between a lower portion of the rear wall of the water tub and the outer cabinet. Consequently, the dead space can effectively be used.